1. Field of the Invention
The present invention relates to a thin-film magnetic head comprising at least an inductive electromagnetic transducer, a method of manufacturing the same, a head gimbal assembly, and a hard disk drive.
2. Related Background Art
In recent years, the areal density of hard disk drives has been improving remarkably. Most recently, the areal density of hard disk drives has reached 160 to 200 Gbytes/platter in particular and is about to exceed this level. As a consequence, thin-film magnetic heads are required to improve their performances.
Widely used as a thin-film magnetic head is a combination thin-film magnetic head having a structure in which a recording head comprising an inductive electromagnetic transducer for writing and a reproducing head comprising a magnetoresistive device (hereinafter also referred to as MR device) for reading are laminated.
In this kind of combination thin-film magnetic head, the recording head comprises a medium-opposing surface (also referred to as air bearing surface or ABS) opposing a recording medium, a lower magnetic pole layer, an upper magnetic pole layer, a recording gap layer, and a thin-film coil, in general. The lower and upper magnetic pole layers have respective magnetic pole parts (opposing magnetic pole parts) opposing each other on the side of medium-opposing surface, and are magnetically connected to each other by a junction disposed at a position separated from the opposing magnetic pole parts. The recording gap layer is formed between the opposing magnetic pole parts. The thin-film coil is insulated from the lower and upper magnetic pole layers and is at least partly disposed therebetween.
For improving performances of the recording head, such as its recording density in particular, its recording medium is required to improve track density. To this aim, a recording head having a narrow track structure in which the track width, i.e., the width between the two opposing magnetic pole parts on the medium-opposing surface, is reduced so as to range from several microns to submicrons, must be realized, whereby the recording head is manufactured by using a semiconductor processing technologies.
As the track width is made smaller, it becomes harder to generate a magnetic flux with a high density between the two opposing magnetic pole parts, whereby a magnetic material having a high saturated magnetic flux density is desired to be used as a material for the magnetic pole parts.
On the other hand, as the frequency of recording signals becomes higher along with the improvement in recording density, the recording head is required to improve the rate at which the magnetic flux changes, i.e., shorten the flux rise time. It is also necessary for the recording head to reduce the deterioration in recording characteristics such as overwrite characteristic and non-linear transition shift in high frequency bands.
For improving the recording characteristics in high frequency bands, it is desirable that the magnetic path length of the recording head be reduced, so as to be able to follow rapid changes of recording signals which have a high frequency and are likely to change fast. The magnetic path length is mainly determined by the length (hereinafter referred to as “yoke length”) from the medium-opposing surface to the junction in the lower or upper magnetic pole layer, whereby reducing the yoke length is effective in shortening the magnetic path length. When a thin-film coil is wound between the medium-opposing surface and the junction, shortening the pitch in the part of windings of thin-film coil disposed between the medium-opposing surface and the junction (hereinafter referred to as “winding pitch”) is effective in reducing the yoke length.
Conventional thin-film magnetic heads have roughly been categorized into those comprising a flat spiral thin-film coil wound about a junction (see the following Patent Document 1), and those (see the following Patent Documents 2, 3, and 4) comprising a thin-film coil helically wound about at least one of the lower and upper magnetic pole layers.
The former thin-film magnetic heads generate most of magnetic fluxes in the vicinity of the junction, and record information with the part of magnetic fluxes guided to the opposing magnetic pole parts by the lower and upper magnetic pole layers. Since most of magnetic fluxes are generated about the junction in the former thin-film magnetic heads, however, only about a few percent of the generated magnetic fluxes is used for recording, so that the recording with magnetic fluxes is not carried out efficiently. Therefore, in order to increase the magnetic fluxes used for recording, the former thin-film magnetic heads have increased the number of turns of the thin-film coil as much as possible. Conventionally known as an example of techniques therefor is one reducing the winding pitch by providing the windings of a second coil between the windings of a first coil (see the following Patent Document 5).
In the latter thin-film magnetic heads, since the thin-film coil is disposed near the medium-opposing surface, generated magnetic fluxes are used for recording more efficiently than in the former thin-film magnetic heads. Therefore, the latter thin-film magnetic heads can make the number of turns of the thin-film coil smaller than that in the former thin-film magnetic heads having a flat spiral thin-film coil, and thus is useful for shortening the yoke length.
In each of the former and latter thin-film magnetic heads, shortening the yoke length is effective in improving recording characteristics in the high frequency band, and making the winding pitch of the thin-film coil as small as possible is effective for realizing this. Increasing the number of turns of the thin-film coil is also effective for increasing magnetic fluxes used for recording. For realizing all of them, it is necessary for making the winding pitch as small as possible, so as to shorten the yoke length, thereby allowing the thin-film coil to increase its number of turns. To this aim, the thin-film coil is required to narrow the width of each turn (turn width).
However, narrowing the turn width in the thin-film coil raises the ohmic value of the thin-film coil, thereby increasing the heat generated from the thin-film coil. When the heat generated from the thin-film coil increases, the thin-film coil expands itself because of the heat. As a consequence, the magnetic pole parts project toward the recording medium, and are likely to collide with the recording medium. Therefore, conventional thin-film magnetic heads have been unable to make the turn width so small. Hence, they have failed to shorten the yoke length.
Conventionally, thin-film coils have been formed by frame plating. A frame used in frame plating includes a wall part disposed between each pair of turns. The wall part must have a certain extent of width in order to keep its shape, which makes it difficult to reduce the interval between adjacent turns (turn interval) when forming a thin-film coil by frame plating.
Patent Document 1: U.S. Pat. No. 6,043,959
Patent Document 2: U.S. Pat. No. 5,995,342
Patent Document 3: Japanese Patent Application Laid-Open No. 2000-311311
Patent Document 4: U.S. Pat. No. 6,459,543B1
Patent Document 5: U.S. Pat. No. 6,191,916B1